It is the long-term objective of the study to investigate the basic biophysical nature of the human tear film, to examine the effects of the presence of a contact lens upon this fluid layer, and determine correlations between these effects and the physiological consequences to the anterior segment of the eye. More specifically, the study will determine the interactions of the in-vivo tear fluid with hydrogel contact lenses and correlate this interaction with the wetting performance, in-eye desiccation, rate and type of lens surface deposits and problems associated with lens wear. This knowledge will aid in understanding the underlying reasons why such complications occur. Despite conjecture and opinion, it is not known with certainty what major factors make overnight wear of hydrogel lenses significantly more prone to complications. Over 4 milion people in the U.S. use extended-wear soft contact lenses, and over 9 million use daily-wear soft contact lenses. Many eye-care practitioners believe, largely based upon their personal experience, that such complications as giant papillary conjunctivitis (GPC), infection, corneal ulceration, etc. are more prominent with this type of lens than with the rigid gas permeable materials. The advent of extended-wear modalities signigicantly exacerbated the occurrence of anterior segment complications, as substantiated by several recent reports in the medical literature that dealt with large numbers of patients. It was found and reported that the users of extended-wear lenses who wore them overnight had a risk 20 to 15 times as great as the usets of daily-wear lenses who did not wear them overnight, and the users of daily-wear lenses who sometimes wore them overnight had nine times the risk of the users of such lenses who did not wear them overnight. The inescapable conclusion was that soft contact lenses worn overnight carry a significantly greater risk for ulcerative karatitis than soft lenses worn only during the day. In this study, two types of daily wear soft contact lenses will be compared with two types of disposable lenses worn on both a daily-wear (with 2-week replacement) and extended-wear (with 1-week replacement) basis. The same patients will use al lens types and wearing modalities. It will be determined how the factors of lens type (daily-wear only vs. disposable), cleaning/disinfection (for daily wear), and wearing conditions (daily vs. extended wear) affect the in-vivo interactions between the tear fluid and the lens surfaces and the physiological response of the eye and lids to that wear. This response will be monitored in terms of changes in the surface wetting of the lenses, their in-eye desiccation, changes in corneal thickness and corneal endothelial cell density, size, and polymegathism, and other problems of the anterior segment. The key feature of the methodology is the use of the tear film interferometer developed by the Principal Investigator. Its use has been notably successful and effective in allowing the actual visualization of the in-vivo tear film and its interactions with contact lens surfaces.